Silk screens, also known in the art as screen stencils and printing screens, reside in a well-established and developed art, such screens being employed in a wide variety of ways for imprinting textiles, completed items of clothing, producing poster art, graphic art, circuit boards, and so forth. As a term of convenience, and as is customarily employed in the art, "silk screen" shall be used herein to denote any type of stenciling item of the type described and of whatever material made. Commonly, silk screens have a metal, e.g. aluminum, or wood frame which clamps into its central opening a fabric such as a polyester fabric comprising the screening element. There are several methods extant for producing a stencil on the screen. One method is to apply a light-sensitive emulsion to one or both sides of the screen element, as by means of a squeegee or another suitable applicator; subsequently, an image is shot onto the emulsion in a camera room and the screen is then taken to a washout booth. The sensitized areas of the emulsion remain, and the remaining emulsion is simply washed out. There are other ways, of course, in applying a stencil to a silk screen, as by other types of substitute materials for the emulsion, whether chemical or otherwise, and may include simply cut-out film strips, and so forth. In making up the pre-press screen, i.e., before it goes "to press", it is preferable to tape the screen by a conventional masking tape or other suitable materials, proximate the frame and especially the frame corners, this so that when the silk screen is to be cleaned, water jets will not have to be directed to the frame corners that might produce unwanted splashing.
Silk screens are expensive, and the user almost always will wish to reclaim the screens if possible for additional uses once a press run has been made. Much of the taping can be removed simply by hand; however, little flecks of tape may still remain on the screen. Also, there is the very formidable matter of removing the stencil, i.e., the used sensitized emulsion areas, and also the inks that have been employed in the printing process. Further media is used for printing, i.e. inks, illuminescent substances, dyes, and so forth, the same are generally soluble only in certain types of non-acqueous chemical solvents. Indeed, it is a great chore to remove the emulsion, masking tape specks, and inks even with the employment of solvents, strippers, and so forth. Additionally, federal and state agencies, in attempting to obviate hazardous working conditions for employees and being concerned with environmental protection, frequently have very stringent rules for the employment of solvents, and it has become increasingly difficult for the silk screen industry to operate under such constraints. It will of course be highly desirable for a system to be devised wherein simply water alone, without the employment of strippers, solvents, and the like, can be used in cleaning silk screens effectively. Prior to this invention this has simply not been possible.
Certain U.S. patents are noted for general purposes of high-pressure cleaning in other arts. These are as follows: U.S. Pat. Nos. 3,147,767, 4,112,535, 3,360,400, 4,350,174, 4,603,661.
The above enumerated patents are relevant as to the principle of power washing in general but are employed in non-analogous arts to the silk screen art. Thus, methods for cleaning walls of a vehicle, see Wild, U.S. Pat. No. '535 above identified,have employed liquid pressures approximating the pressure necessarily used by the inventor herein in cleaning silk screens. Others of the patents, however, relate simply to cleaning slag deposits from cyclone burners, the interiors of nuclear power equipment, castings, and so forth.
As to the methods and apparatus for cleaning silk screens: three patents, these being U.S. patents, are known to the inventor, which are identified as follows: Key U.S. Pat. Nos. 3,580,261, Black, et al 3,656,493, Jensen 4,420,004.
All of the above patents are relative insofar as jet spray cleaning of silk screens are concerned. All of these patents, however, use closed cabinets and elaborate means for spraying, solely interiorly of such cabinet, the screens within. There is no teaching in any of these patents of spraying from a point exterior to the cabinet. Nor is there any teaching that water alone can be used to reclaim the screens provided, whereas in the present invention, the water is maintained within a range of elevated temperatures and pressure so as to avoid completely the otherwise necessary employment of solvents, strippers, detergents, and the like. Thus, in the present invention, the environmental impact of use of the equipment is minimized if not eliminated. Reservoirs of cleaning fluids have heretofore been employed, as for example, in the Key U.S. Pat. No. '261 above cited. However, the cleaning media constitutes a highly flammable solvent, a stripper, or the like. There is no provision in any of the above patents for a closed water system and sophisticated filtering system wherein the water coming from the spraying step may be filtered and recycled for further use. Additionally, as is hereinafter pointed out, a bypass system is included such that the pump accommodating the present invention may be running continuously while the spray gun employed is actuated intermittently.